1. Field of the Invention
The present invention relates to an air conditioning apparatus having a water heat exchanger unit.
2. Description of the Related Art
An air conditioning apparatus has one outdoor unit and one or a plurality of indoor units. The outdoor unit has a compressor, a four-way valve, a water heat exchanger unit, and a expansion valve. Each indoor unit has an air heat exchanger.
In this air conditioning apparatus, the compressor, the four-way valve, the water heat exchanger unit, the expansion valve, and one or the plurality of air heat exchangers are connected via pipes, thus constituting a heat pump type refrigeration cycle.
When the compressor is operated and the four-way valve is set in the neutral state, the refrigerant discharged from the compressor flows to the water heat exchanger unit via the four-way valve, and the refrigerant output from the water heat exchanger unit returns to the compressor via the expansion valve, one or the plurality of air heat exchangers, and the four-way valve. That is, the water heat exchanger unit serves as a condenser, and one or the plurality of air heat exchangers serve as evaporators, thus executing a cooling operation mode.
When the compressor is operated and the four-way valve is switched, the refrigerant discharged from the compressor flows to one or the plurality of air heat exchangers via the four-way valve, and the refrigerant output from one or the plurality of air heat exchangers returns to the compressor via the expansion valve, the water heat exchanger unit, and the four-way valve. That is, one or the plurality of air heat exchangers serve as condensers, and the water heat exchanger unit serves as an evaporator, thus executing a heating operation mode.
The water heat exchanger unit exchanges heat of the refrigerant flowing therein for heat of water supplied by an external water supply unit. The air-conditioning capability is increased by this water heat exchanger unit.
The expansion valve include cooling and heating expansion valves. A heating expansion valve for the heating operation mode has a heat-sensitive portion for sensing a temperature of the refrigerant taken into the compressor. The opening degree of the heating expansion valve is automatically changed in accordance with a difference between the temperature of the refrigerant flowing into the heating expansion valve and the temperature sensed by the heat-sensitive portion.
A super-heat degree of the refrigerant in the water heat exchanger unit is kept at a predetermined value by the change in opening degree of the expansion valve. This is to maintain a stable operation of the components constituting the refrigeration cycle.
When the temperature of water supplied to the water heat exchanger unit is increased, the temperature of the refrigerant flowing from the water heat exchanger unit is increased. Then, the heat-sensitive portion of the expansion valve is heated.
When the heat-sensitive portion of the expansion valve is heated, the opening degree of the expansion valve is increased to increase the flow rate of the refrigerant, thus increasing a low-pressure-side pressure of the refrigeration cycle. Then, a high-pressureside pressure is also increased accordingly.
When the high-pressure-side pressure is excessively increased, the lifetime of the components constituting the refrigeration cycle is adversely affected.
A lubricant for smoothing motion of the components is filled in the compressor. Part of the lubricant flows into the refrigeration cycle together with the discharged refrigerant, but is returned to the compressor together with the refrigerant.
In an air conditioning apparatus having a plurality of indoor units, however, the capability of the compressor is controlled in accordance with the sum of the air conditioning loads of the indoor units. Therefore, when the number of operating indoor units is small, the circulating amount of refrigerant is decreased.
When the circulating amount of refrigerant is decreased, the amount of lubricant returning to the compressor is decreased, thus adversely affecting the lifetime of the compressor.
For this reason, conventionally, an operation for increasing the capability of the compressor is periodically executed during the cooling operation mode. That is, when the capability of the compressor is increased, the circulating amount of refrigerant is increased, so that the lubricant in the refrigeration cycle is forcibly recovered to the compressor.
During recovery, however, as the flow rate of refrigerant is increased, the vapor pressure of the refrigerant in the water heat exchanger unit is decreased. Then, the low-pressure-side pressure of the refrigeration cycle is decreased, and a pressure switch connected to the low-pressure-side pipe is sometimes operated.
The pressure switch is provided for protecting the low-pressure-side pipe against an abnormal pressure drop and for preventing freezing of the water heat exchanger unit during the heating operation mode. When the pressure switch is turned on, operation of the compressor is stopped.
Then, the cooling operation is sometimes unnecessarily stopped.
Published Unexamined Japanese Patent Application No. 64-6657 discloses an air conditioning apparatus having a plurality of indoor units.
In this air conditioning apparatus, one outdoor unit has a plurality of air heat exchangers 3 and 4, and a plurality of indoor units 8 and 9 have air heat exchangers 11a and 11b, respectively. A flow of the refrigerant into the air heat exchangers 3 and 4 is controlled in accordance with the number of operating indoor units.
This air conditioning apparatus, however, has no water heat exchanger unit.
Published Examined Japanese Utility Model Application No. 54-685 discloses an air conditioning apparatus having a plurality of indoor units and a water heat exchanger unit.
This air conditioning apparatus, however, has no control concerning the super-heat degree of the refrigerant in a water heat exchanger unit 3 and not control concerning recovery of the lubricant.